1. Field of the Invention
The present invention relates to an engine system in which exhaust gas is re-circulated by using a turbocharger for improving an output in a low speed range, increasing combustion efficiency, and improving an exhaust gas quality.
2. Description of Related Art
In general, it is known that a diesel engine may have fuel consumption lower than a gasoline engine and efficiency better than the gasoline engine. In general, the diesel engine displays efficiency in a range of 40% owing to a high compression ratio of the diesel engine.
Currently, in order to obtain a high output from the engine, the engine is provided with the turbo charger and an inter cooler, additionally.
The engine having the turbo charger applied thereto thus intakes the exhaust gas or external air with a compressor in the turbo charger and supplies supercharged air (High temperature compressed air) produced thereby to an engine side.
However, the air compressed rapidly absorbs heat from the turbo charger and heat generated in a course of the compression so as to be involved in drop of density, resulting in poor charging efficiency. Therefore, the supercharged air is cooled by using the intercooler to obtain high density, resulting to intake much air into an engine combustion chamber, enabling to obtain a high output.
In the meantime, currently, meeting the exhaust gas control trend, such as EURO 3 or EURO 4 of the Europe, a variety of systems are suggested, in which a portion of the exhaust gas containing CO, HC, NOx, and so on being exhausted from a turbo diesel engine is re-circulated for reducing contents thereof further. Of the systems, typical one is an EGR System (Exhaust Gas Recirculation System).
Along with this, a research is underway, in which an output torque is increased while reducing the fuel consumption in medium to low speed ranges of engine RPM in the engine having the turbo charger, and a research is also underway for making efficient control of the supply of the re-circulated gas.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.